Photosynthesis is the process by which plants capture energy from sunlight and use it to produce food. It occurs in two stages: in the first stage, chloroplasts in plant cells absorb sunlight using the pigment chlorophyll, and in the second stage they use the captured energy to convert carbon dioxide and water into oxygen and sugars. Plants take in carbon dioxide through pores called stomata and water through their roots, and the chemical reaction takes place inside the chloroplasts using energy from sunlight to produce oxygen as a byproduct and sugars that the plant stores as food.

1. Chapter 4, Section 1
Cell Processes and Energy
PHOTOSYNTHESIS

2. KEY IDEA
How do cells obtain
the energy they need
to carry out their
functions?

3. Photosynthesis • The process by which a
cell captures energy in
sunlight and uses it to
make food
• Nearly all living things
depend on the energy
of the sun

4. The Two Stages of Photosynthesis
STAGE 1: Capturing the sun’s • The sun’s energy is taken in by
energy the leaves of a plant
• This is done by the
photosynthetic pigment,
chlorophyll, in the chloroplasts
Chloroplasts in a plant cell of the plant cell
• CHLOROPHYLL gives plants their
GREEN color
• This energy is then used in the
second step of photosynthesis

5. STAGE 2: Using energy to • The captured sun energy is
make food used to make sugars and
oxygen from water and
carbon dioxide.
• The plant roots take in
water (H₂O) from the soil
• Tiny pores on the leaves,
called stomata, take in
carbon dioxide (CO₂) from
the air
• Once in the leaves, the H₂O
and CO₂ move into the
chloroplasts in the cells
Magnified stomata in a pine needle Table Talk: What do
stomata remind you of in
the human body?

6. Table Talk: Summarize the
two stages of
photosynthesis

8. What happens to the • Plants use some of it for
sugar produced in food
photosynthesis?
• Some sugar molecules are
converted into other
compounds such as
cellulose, which is used to
form the plant cell wall
• Other sugar molecules are
stored in the plant’s cells for
later use
• When we eat fruits and
vegetables, we are eating
the plant’s stored energy

9. QUICKWRITE: SUMMARIZE
In your own words, write a short paragraph describing the
process of photosynthesis. Include and underline the
following words:
Carbon dioxide
Water
sugar
Oxygen
Photosynthesis
Sunlight
Chloroplasts
stomata
See BrainPop, “Photosynthesis” end